light tight exhaust??

how can i make my exhaust light tight for my cab?

light wont bend so 2 90 degree elbows with the inside painted black will work.

Sort of depends on how your cab is setup/constructed. Generally speaking a light trap can be made by creating a few 90 degree bends though there are many ways to accomplish it. I'd need to know about your setup to recommend something specific. Materials used and their reflectivity, space available, stealth considerations (if any) will all influence your solution.